What is setHours() in JavaScript?

The setHours function in JS is a method of the Date class with the following syntax:

setHours(hoursValue)
setHours(hoursValue, minutesValue)
setHours(hoursValue, minutesValue, secondsValue)
setHours(hoursValue, minutesValue, secondsValue, msValue)

Parameters

hoursValue is an integer value from 0 to 23 (representing time in 24-hour clock format). A value greater than 23 is added as extra hours to the date object.
minutesValue is an integer value from 0 to 59 that represents minutes. A value greater than 59 is added as extra minutes to the date object.
secondsValue is an integer value from 0 to 59 that represents seconds. A value greater than 59 is added as extra seconds to the date object.
msValue is an integer value from 0 to 999 that represents milliseconds. A value greater than 999 is added as extra milliseconds to the date object.

Note: Only the hoursValue parameter is required, the rest are optional.

Return value

setHours returns the number of milliseconds elapsed since 1 January 1970 00:00:00 UTC till the updated time.

The setHours function is called on a Date object, which results in the specified parameters being changed in the Date object.

Example

The following code demonstrates the usage of the setHours function:

let d1 = new Date('June 29, 2021 15:39:05:32');
let d2 = new Date('June 29, 2021 15:39:05:32');
let d3 = new Date('June 29, 2021 15:39:05:32');
let d4 = new Date('June 29, 2021 15:39:05:32');
console.log('Dates Before Changing:');
console.log('d1: ', d1);
console.log('d2: ', d2);
console.log('d3: ', d3);
console.log('d4: ', d4);
d1.setHours(8);
d2.setHours(8, 8);
d3.setHours(8, 8, 8);
d4.setHours(8, 8, 8, 8);
console.log('Dates After Changing:');
console.log('d1: ', d1);
console.log('d2: ', d2);
console.log('d3: ', d3);
console.log('d4: ', d4);